1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and particularly to an ink jet recording apparatus used as an apparatus for outputting characters and images in facsimiles, copy machines, printers and others.
2. Description of the Related Art
Non-impact recording methods have been remarkably put into practical use on the basis that the level of noise generated by recording operations could be kept so low that their existence could be neglected. Among several kinds of non-impact recording methods, ink jet recording method is one of the most advantageous methods where general purpose paper sheets can be used for recording without processing their own material and/or coating specific synthetic materials on their surfaces.
In a recording head used in the ink jet recording apparatus, in general, there exists an ink fluid path having an orifice at one open end, an energy supplying part formed in a part of this ink fluid path and an energy generation means for generating energy to be supplied to ink fluid in the energy supplying part so as to eject ink fluid.
As for energy generation means, what can be selected are electromechanical conversion devices such as piezo device, electromagnetic wave energy generation means such as lasers which apply electromagnetic waves to the ink fluid for the generation of heat and eject the ink fluid by kinetic energy accompanied by the heat generation, and electrothermal conversion devices discharging the ink fluid by heating the ink fluid with heating resistors.
Among these devices and means, recording heads using electro-thermal conversion devices as energy generation means can be formed with orifices arranged in a high density array, and therefore, with these devices, a high resolution recording can be achieved. In addition, the size of the finished recording head can be small and recent technical advantages in semiconductor devices and their fabricating processing technologies can be fully used in order to develop recording heads in large-scale and two-dimensional configurations. By using electro-thermal conversion devices, the fabrication in large amounts and with low cost of recording heads having a relatively large number of orifices formed with a high density and an ink jet recording apparatus with such recording heads are feasible.
In ink jet recording heads, there may be cases that the viscosity of ink fluids may increase due to evaporation of water or other solvents in ink fluids especially when a long period of time has passed since the recording operation was terminated or when some orifices are not used for recording operations owing to characteristic patterns of the recorded images. As a result, the amount of ink fluid ejected from such an orifice may be lowered and the ejecting direction of ink fluids may become unstable, and in the worse cases, the ejection operation may fail due to plugging of the orifice. One of the structures used in order to prevent such ejection operation failures is a capping mechanism having a cap for covering the orifice of the recording head. With this capping mechanism, by capping the recording head not used in the recording operation, the orifice is shielded from the atmosphere and the increase of the viscosity of ink fluids in the orifice can be prevented. However, as for an orifice which is not used for ejecting ink fluids during the recording operation, even in the recording operation, the ink fluid may become more viscous which may lead to the ink fluid ejection failure. Such ink fluid ejection failure can be prevented by a structure where an ink fluid ejection operation is performed independently of recording operations. This ink fluid ejection operation is called idle ejection in the following description.
In the idle ejection operation, it is general that a storage part for storing the ink fluid ejected from the orifice is provided. One embodiment of the storage part is an ink absorber made of porous materials for absorbing the waste ink fluid ejected from the orifice. The ink absorber is placed in front of the orifice and linked to the waste ink fluid storage tank installed in a designated position for receiving and storing waste ink fluids through flexible tubes. In many cases, the above described capping means has an ink absorber inside.
One embodiment of idle ejection operations using the cap having an ink absorber is disclosed in Japanese Patent Application Laying-open No. 227654/1991 which is published after the priority date of this application. The recording head disclosed in this gazette has orifices along the range corresponding to a width of the recording sheet being transported in the apparatus, and the recording operation is performed by moving the recording sheet relative to the recording head which are fixed in the apparatus. The idle ejection operations in this recording head are performed in the following manner.
In the case where the idle ejection is performed during the recording operations, after the recording head unit is moved upward, the cap unit is moved in the horizontal direction to the original position of the recording head. Next, the recording head unit is moved downward so that the cap unit may contact the recording head unit and the ink fluids in the recording head is ejected to the ink absorber in the cap by the idle ejection operation. After completing the idle ejection operation, the recording head unit is moved backward to the original position for the recording operation.
The above-mentioned ejection operation is basically applicable to the case that the recording head moves relative to the recording sheet in the recording operation. That is, the recording head unit is moved to the position where the cap unit is fixed and the recording head unit and the cap unit are caused to contact each other for the capping operation. While the cap unit contacts the recording head, the idle ejection operation continues, and after completing the idle ejection operation, the recording head unit is moved backward to the recording positions.
In either of the above-mentioned methods, the idle ejection operation is often performed just before starting the recording operation after waiting for the recording operation, with the recording head being capped as well as concurrently during the recording operation.
The above described idle ejection operation accompanies the movement of the recording head unit and the cap unit toward the positions for the idle ejection operation and the movement of the recording head unit and the cap unit back to the positions for the recording operation, and the time spent accomplishing these movements is one of major factors reducing the throughput of the ink jet recording apparatus.